The present invention relates generally to the field of medical equipment for evaluating muscle performance. More particularly, the present invention relates to a method for determining back muscle dysfunction.
Electrical activity measurements as a measure of muscle activity, electromyographic (EMG) measurement, may be performed using invasive or non-invasive techniques. EMG measurements are used in number of different medical applications.
The use of invasive percutaneous EMG has widespread medical acceptance as an accurate technique for measuring electrical activity of an underlying muscle. However, invasive techniques are often not easily usable. That is, invasive techniques require additional materials, expertise, and risk not found with non-invasive techniques.
Measuring muscle activity using surface EMG (sEMG) measurements has attracted interest in scientists and medical practitioners for the last 30 years with its promise as an objective non-invasive muscle measurement technique. Considerable effort has been expended researching the application of EMG measurements (both percutaneous and non-invasive) in the treatment and possible diagnosis of low back pain. An extensive body of scientific literature now exists describing the use of EMG measurements.
Measurements of surface electrical activity, or any other clinical measurement, must meet several objectives and criteria relating to reliability in order to obtain useful diagnostic or evaluative information. For example, the electrical activity signal measured must be objectively defined and reproducible. The information obtained must meet a need which is best obtainable by using the surface EMG technique. Further, the information must be usable and easily interpreted by the level of skill of practitioners for which it is intended. And, finally, the process must be cost effective and have universal application as either an assessment or therapeutic system or both.
In order to meet these objectives the evaluation system must reliably differentiate between healthy normal pain free subjects and subjects with muscle disorders and report results with an extremely high level of statistical certainty. Of the many possible uses to which surface EMG may be applied, back function evaluation is highly suitable. A relatively large percentage of individuals experience back pain which could be attributed to soft tissue damage, i.e., muscle dysfunction. Typical evaluation techniques are not able to objectively determine the muscle dysfunction responsible for the pain.
Typical clinical evaluation techniques have relied upon subjective evaluations by the patient to determine the nature of the dysfunction. That is, the patient is asked to perform certain motions, and depending upon the patient's ability to perform these motions within subjective pain parameters a diagnosis is generated.
Further, from an economic standpoint a large percentage of insurance claims are made by individuals claiming to have muscle back pain. Because of the subjective nature of the testing, these claims cannot be objectively verified. Accordingly, there is a large potential for fraudulent claims being filed at a substantial cost to insurance companies.
In order to provide an effective assessment system there must be a capability of making significant comparisons of the individual to a normative group. In order to make these comparisons the coefficient of variation, the standard deviation/mean, must lie in the 10%-30% range. Accordingly, it is extremely important that a system have reproducible data.
In the past, studies which have attempted to achieve the reproducibility or minimize the variation in data use a maximum voluntary contraction (MVC) method of normalization. This technique requires high levels of activation and causes the engagement of fast twitch motor units not ordinarily activated in normal movements. That is, these studies compare the measured muscle activity during evaluation to a maximum voluntary contraction.
In normal muscle the slow twitch motor units produce most of their fused tension before fast twitch motor units start to add to muscle force. Addition of fast twitch motor units in MVC causes a disproportionate increase in the surface EMG. The inclusion of fast twitch motor units, which are seldom used in everyday functioning, occurs with the MVC condition and influences the anatomical distribution and force-voltage relationship of EMG data. Moreover, MVC runs the risk of exacerbating pain and doing further damage to dysfunctional muscles.
Clinical use of surface EMG has failed to produce a sufficiently objective evaluation of muscle health. In much of the covering literature relating to back muscle evaluation, an equivalence is sought between EMG resting levels and painful muscles or back pain in general. However, static resting measurements are greatly influenced by small postural adjustment that cannot be adequately controlled. Accordingly, the postural and instrumental error can become so large so as to obscure useful information.
Accordingly, there is a need to develop a system for correctly detecting muscle dysfunction with a high degree of reproducibility. Further, this method also must allow for normalization of data using normally activated muscle values.